Valve including a step-up piston for controlling fluids

ABSTRACT

A valve for controlling liquids for its actuation is provided with a liquid-filled coupling chamber, which is disposed between a step-up piston, actuatable by a piezoelectric actuator, and a piston that actuates a valve member. To compensate for leakage in the coupling chamber that is at high pressure, a filling valve is provided. The filling valve is disposed between the step-up piston and the piezoelectric actuator. Upon each return stroke of the piezoelectric actuator, the step-up piston follows the piezoelectric actuator with a time lag, so that the filling valve opens briefly and allows filling of the coupling chamber. The valves intended for use in fuel injection systems for internal combustion engines of motor vehicles.

PRIOR ART

The invention relates to a valve for controlling liquids. One such valveis known from European Patent Disclosure EP 0 477 400. There, theactuating piston of the valve member is disposed, tightly displaceably,in a smaller-diameter portion of a stepped bore, while conversely alarger-diameter step-up piston, which is moved with the piezoelectricactuator, is disposed in a larger-diameter portion of the stepped bore.

Between the two pistons, a hydraulic chamber is enclosed in such a waythat when the step-up piston is moved a certain distance by theactuator, the actuating piston of the valve member is moved by adistance that is increased by the step-up ratio of the stepped borediameters. The valve member, actuating piston, larger-diameter step-uppiston, and piezoelectric actuator are all located on the same axis.

In such valves, the problem exists of compensating for changes in lengthof the piezoelectric actuator, the valve, or the valve housing, by meansof the hydraulic coupling chamber. Since the piezoelectric actuator, foropening the valve, generates a pressure in the coupling chamber, thispressure also leads to a loss of coupling chamber liquid. To prevent thecoupling chamber from being pumped dry, it must be refilled. A devicethat is intended to accomplish such refilling is already known from theprior art named at the outset, but this prior art has the disadvantagethat a connection between the coupling chamber and a supply containerthat is constantly open in both possible flow directions is provided,which significantly affects the operating performance of thepiezoelectric actuator. In particular, a thus increased volume leads toa compressibility that reduces the transmission rigidity of thehydraulic column formed by the coupling chamber.

ADVANTAGES OF THE INVENTION

The valve of the invention has an advantage over the prior art thatfilling of the coupling chamber is attained in a simple way via a valvefunction, and thus the step-up piston and the piston that actuates thevalve always remain at the same spacing from one another. It is alsoadvantageous that filling of the coupling chamber can be attained bysimple means.

BRIEF DESCRIPTION OF THE DRAWINGS

One exemplary embodiment of the invention is shown in the drawings anddescribed in further detail below. Shown are:

FIG. 1, a fuel injection valve in section;

FIG. 2, a piston arrangement at a coupling chamber; and

FIG. 3, a pressure graph.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

The valve of the invention is used in a fuel injection valve, which isshown in its essential parts in section in FIG. 1. This injection valvehas a valve housing 1, in which a valve needle 3 is guided in alongitudinal bore 2. This valve needle may also be prestressed by aclosing spring in the closing direction in a known manner, not shown infurther detail here. On one end, the valve needle is provided with aconical sealing face 4, which cooperates at the tip 5 of the valvehousing protruding into the combustion chamber with a seat 6, from whichinjection openings lead away. In the interior of the injection valve, inthis case, the annular chamber 7 surrounding the valve needle 3 andfilled with fuel at injection pressure communicate with the combustionchamber, so as to execute an injection when the valve needle has liftedfrom its seat. The annular chamber communicates with a further pressurechamber 8, which is in constant communication with a pressure line 10 byway of which the fuel injection valve is supplied with fuel at injectionpressure from a high-pressure fuel reservoir 9. This high fuel pressureis also operative in the pressure chamber 8 and there acts on a pressureshoulder 11, by way of which in a known manner the nozzle needle can belifted from its valve seat, under suitable circumstances.

On the other end of the valve needle, the valve needle extends into acylinder bore 12, where with its end face 14 it encloses a controlpressure chamber 15, which communicates constantly via a throttleconnection 16 with an annular chamber 17, which like the pressurechamber 18 is always in communication with the high-pressure fuelreservoir. A throttle bore 19 leads axially away from the controlpressure chamber 15 to a valve seat 20 of a control valve 21.Cooperating with the valve seat is a valve member 22 of the controlvalve, which in the state where the valve is lifted from the valve seatestablishes a communication between the control pressure chamber 15 anda spring chamber 18, which in turn communicates constantly with a reliefchamber. A compression spring 24 that urges the valve member 22 in thecontrol valve is disposed in the spring chamber 18 and urges the valvemember 22 onto the valve seat 20, so that in the normal position of thecontrol valve, this communication with the control pressure chamber 15is closed. Since the area of the face end of the valve needle 3 in theregion of the control pressure chamber is larger than the area of thepressure shoulder 11, the same fuel pressure in the control pressurechamber, which also prevails in the pressure chamber 8, now keeps thevalve needle 3 in the closed position. Once the valve member 22 haslifted away, however, the pressure in the control pressure chamber 15,decoupled via the throttle connection 16, is relieved. With the closingforce now absent or reduced, the valve needle 3 opens quickly,optionally counter to the force of a closing spring, and on the otherhand can be brought into the closing position as soon as the valvemember 22 returns to its closing position, since from that moment on,via the throttle connection 16, the original high fuel pressure in thecontrol pressure chamber 15 is rapidly restored.

The control valve of the invention has a piston 25, which is intended toactuate the control valve and acts on the valve member 22 and is in turnactuatable by a piezoelectric actuator 22. The piston 25 is guided in aguide bore 28, at the cost of a guide gap 33, and with its end face 29defines a coupling chamber 30, which is closed off on its opposite wallby a step-up piston 35 of larger diameter; this step-up piston 35 isactuated by a piezoelectric actuator 32 and is kept in contact with thepiezoelectric actuator 32 by a spring washer 41 disposed in the couplingchamber 30. The step-up piston 35 is guided in a housing bore 46 and hasa guide gap 45 relative to this bore.

The coupling chamber 30, because of the different areas of the twopistons 25 and 35, serves as a step-up chamber, by stepping up astructurally dictated short stroke of the piezoelectric actuator 32 to alonger stroke of the piston 25 that actuates the control valve 21. Uponexcitation of the piezoelectric actuator 32, the piston 25 is adjustedin such a way that the valve member 22 is lifted from its seat 20. Theresult of this is a relief of the control pressure chamber, which inturn causes the valve needle 3 to open.

The piezoelectric actuator 32 has an end 34, oriented toward the valvemember 22, which dips into an axial bore 43 of the step-up piston 35.The axial bore 43 leaves an annular cylinder 36 open between itself andthe piezoelectric actuator 32, and this annular cylinder acts as afilling inlet. The axial bore 43 changes over, toward the side of thecoupling chamber 30 via a preferably conical annular shoulder 37, intoan axial filling bore 44, which connects the annular chamber to thecoupling chamber. The annular shoulder 37 is embodied as a valve seat 38for the piezoelectric actuator 32, which together with the valve seatforms a filling valve 39. A lower end 34 of the piezoelectric actuator32 for that purpose has a conical sealing face 40, which comes intocontact with the valve seat and thus interrupts the communicationbetween the coupling chamber 30 and the annular cylinder 36.

The leaf spring 41 in the coupling chamber 30 is braced against ahousing shoulder 42 and seeks to press the step-up piston 35 with itsvalve seat 38 against the sealing face 40 and thus to keep the fillingvalve 39 closed.

A region 47, oriented toward the coupling chamber 30, of the step-uppiston 35 is reduced to a smaller diameter and has a relatively largeplay 48 relative to the housing bore 46. The risk that the step-uppiston 35 will seize in its guide from spreading of the lower,less-rigid region, is thus prevented.

The reciprocation capability of the piezoelectric actuator 32 is veryslight and is stepped up with the aid of the hydraulic stepup via thehydraulic coupling chamber 30 as a longer stroke to the piston 25. Atthe same time, the thermal expansion of the device is absorbed by thishydraulic stepup. Upon compression of the device, a high pressure isgenerated in the coupling chamber 30, and this pressure causes leakageto occur via the guide gaps 33 and 45; this leakage must be compensatedfor again by filling the coupling chamber 30, so that the couplingchamber will not be pumped dry over the course of a plurality ofstrokes.

FIG. 3, with the aid of a graph, shows how the strokes of thepiezoelectric actuator 32 and of the step-up piston 35 have differentcourses over time. Because of its mass and its positive displacement ofliquid, the step-up piston is unable to follow the piezoelectricactuator, which adjusts extremely quickly, with the same speed. In theupper portion of the graph, a curve 49 is shown which plots the travelof the piezoelectric actuator 32; below it is a curve 50 that plots thetravel of the step-up piston 35, which cannot follow the motion of thepiezoelectric actuator simultaneously. The difference in the motion ofthe two pistons is plotted with the dashed line 51 in the lower curveand in the form of a triangular area 52 symbolizes the time frame forfilling.

It can be seen from the graph that in the course of its back-and-forthstroke, the step-up piston 35, tripped in its return stroke by theshortening of the piezoelectric actuator 32, executes a relative motionwith regard to the piezoelectric actuator 32 and in other words has adifferent stroke speed from that of the piezoelectric actuator. Thisresults in lifting of the step-up piston with its valve seat 37 from thepiezoelectric actuator 32 and its sealing face 40 and an opening of thefilling bore 44. This then leads to refilling of the coupling chamber30.

Upon each stroke, and specifically in the closing motion of theinjection valve whenever the piezoelectric actuator is retractedquickly, the refilling takes place so fast that whenever thepiezoelectric actuator is retracted quickly its closing member 40 liftsfrom its valve seat 38 at the step-up piston 35.

Via the now-open filling valve 39, liquid flows through the annularcylinder 36 into the coupling chamber 30. At the end of thereciprocating motion of the two pistons 31 and 35, the filling valve 39is automatically closed again by the spring 41.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

What is claimed is:
 1. A valve for controlling liquids, comprising acontrol valve member (22), which is actuatable counter to a force of acompression spring (24) in the opening direction by a control valvepiston (25), said control valve piston having a face end which closesoff a portion of a hydraulic coupling chamber (30), said hydrauliccoupling chamber (30) having another portion which is defined by a faceend of a step-up piston (35), said step-up piston has a larger diameterthan the control valve piston (25) and is movable in a working stroke bya piezoelectric actuator (32), wherein a pressure increase in thecoupling chamber is generated by the working stroke of the step-uppiston, and as a result of this increase, the control value piston (25)is movable counter to a force of the compression spring (24), in whichthe step-up piston (35) is movable relative to the piezoelectricactuator (32) and together with the piezoelectric actuator forms afilling valve (39), by which filling valve (39) the coupling chamber(30) is made to communicate with a liquid source (36), and, in a courseof a reciprocating motion of the step-up piston (35), the step-up pistonexecutes a movement with respect to the piezoelectric actuator (32). 2.The valve according to claim 1, in which the step-up piston (35) isguided in a housing bore (46), leaving a narrow guide gap (45), and thata lower region (47) of said step-up piston, oriented toward the couplingchamber (30) of the step-up piston (35) is reduced to a smaller outsidediameter, which provides play relative to the housing bore (46).
 3. Thevalve according to claim 1, in which the step-up piston (35) has adifferent stroke speed from the piezoelectric actuator (32), and thatthe speed difference is utilized for opening the filling valve (39) andfor filling liquid into the coupling chamber (30).
 4. The valveaccording to claim 3, in which the step-up piston (35) concentricallysurrounds the piezoelectric actuator (32) at one end (34) of thepiezoelectric actuator oriented toward the control valve member (22) andleaves an annular cylinder (36) open as a filling inlet, said annularcylinder (36) having an inner annular shoulder (37) which provides avalve seat (38), which together with the one end (34) of thepiezoelectric actuator serving as a filling valve (39) which controls afilling bore (44) that connects the annular cylinder (36) with thecoupling chamber (30).
 5. The valve according to claim 4, in which thestep-up piston (35) is urged toward the piezoelectric actuator by theforce of a second spring (41), which is supported on a housing shoulder(42) and, during a return stroke of the piezoelectric actuator (32)causes the step-up piston to follow the piezoelectric actuator.
 6. Thevalve according to claim 4, in which the end (40) of the piezoelectricactuator (32) is shaped so as to close said valve seat (38) of thefilling valve (39).
 7. The valve according to claim 6, in which thestep-up piston (35) is urged toward the piezoelectric actuator by theforce of a second spring (41), which is supported on a housing shoulder(42) and, during a return stroke of the piezoelectric actuator (32)causes the step-up piston to follow the piezoelectric actuator.
 8. Thevalve according to claim 1, in which the step-up piston (35)concentrically surrounds the piezoelectric actuator (32) at one end (34)of the piezoelectric actuator oriented toward the control valve member(22) and leaves an annular cylinder (36) open as a filling inlet, saidannular cylinder (36) having an inner annular shoulder (37) whichprovides a valve seat (38), which together with the one end (34) of thepiezoelectric actuator serving as a filling valve (39) which controls afilling bore (44) that connects the annular cylinder (36) with thecoupling chamber (30).
 9. The valve according to claim 8, in which thestep-up piston (35) is guided in a housing bore (46), leaving a narrowguide gap (45), and that a lower region (47) of said step-up piston,oriented toward the coupling chamber (30) of the step-up piston (35) isreduced to a smaller outside diameter, which provides play relative tothe housing bore (46).
 10. The valve according to claim 8, in which thestep-up piston (35) has a large bore (43), which receives thepiezoelectric actuator (32) and continues to the coupling chamber (30)through the filling bore (44), and that the inner annular shoulder (37)for said valve seat is located at the transition from the large bore(43) to the smaller filling bore (44).
 11. The valve according to claim10, in which the step-up piston (35) is guided in a housing bore (46),leaving a narrow guide gap (45), and that a lower region (47) of saidstep-up piston, oriented toward the coupling chamber (30) of the step-uppiston (35) is reduced to a smaller outside diameter, which providesplay relative to the housing bore (46).
 12. The valve according to claim8, in which the step-up piston (35) is urged toward the piezoelectricactuator by the force of a second spring (41), which is supported on ahousing shoulder (42) and, during a return stroke of the piezoelectricactuator (32) causes the step-up piston to follow the piezoelectricactuator.
 13. The valve according to claim 12, in which them step-uppiston (35) has a large bore (43), which receives the piezoelectricactuator (32) and continues to the coupling chamber (30) through thefilling bore (44), and that the inner annular shoulder (37) for saidvalve seat is located at the transition from the large bore (43) to thesmaller filling bore (44).
 14. The valve according to claim 12, in whichthe step-up piston (35) is guided in a housing bore (46), leaving anarrow guide gap (45), and that a lower region (47) of said step-uppiston, oriented toward the coupling chamber (30) of the step-up piston(35) is reduced to a smaller outside diameter, which provides playrelative to the housing bore (46).
 15. The valve according to claim 8,in which the end (40) of the piezoelectric actuator (32) is shaped so asto close said valve seat (38) of the filling valve (39).
 16. The valveaccording to claim 15, in which the step-up piston (35) is urged towardthe piezoelectric actuator by the force of a second spring (41), whichis supported on a housing shoulder (42) and, during a return stroke ofthe piezoelectric actuator (32) causes the step-up piston to follow thepiezoelectric actuator.
 17. The valve according to claim 15, in whichthe step-up piston (35) has a large bore (43), which receives thepiezoelectric actuator (32) and continues to the coupling chamber (30)through the filling bore (44), and that the inner annular shoulder (37)for said valve seat is located at the transition from the large bore(43) to the smaller filling bore (44).
 18. The valve according to claim15, in which the step-up piston (35) is guided in a housing bore (46),leaving a narrow guide gap (45), and that a lower region (47) of saidstep-up piston, oriented toward the coupling chamber (30) of the step-uppiston (35) is reduced to a smaller outside diameter, which providesplay relative to the housing bore (46).
 19. A control valve forcontrolling liquids, comprising a control valve member (22) which isacted upon by a resilient force of a return spring (24), by means ofwhich the control valve member is brought to a starting position, thecontrol valve member is provided with an actuation piston (25), one sideof the actuation piston delimits part of a wall of a closed couplingchamber (30) filled with a liquid, which closed coupling chamber, atanother part, is further delimited by a side of a step-up piston (35),which side of the step-up piston has a larger end face than the one sideof the actuation piston, and which step-up piston is actuated by apiezoelectric actuator (32), thereby initiating the movement of theactuating piston via the liquid received in the closed coupling chamberagainst the force of the return spring, and moved back by the returnspring upon a respective backward movement of the actuator (32), thestep-up piston having at its side remote from the closed couplingchamber an inner cylinder (43) which is in permanent connection to asource of liquid and which is connectable to the closed coupling chamberby means of a bore (44) in the side of the step-up piston, and in whichthe piezoelectric actuator projects into the inner cylinder (43), cominginto abutment at the inner side of the inner cylinder of the step-uppiston and covering said bore (44) thus closing the connection betweenthe liquid source and the closed coupling chamber, whereas on a quickmovement of the piezoelectric actuator backward off the inner side ofthe step-up piston, the step-up piston is held back a short time becauseof its displacement resistance thereby opening the connection betweenthe liquid source and the coupling chamber via said bore so as toreplace liquid losses from the closed chamber occurring on the movementof said actuating piston (25) and said step-up piston.